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BIOLOGY 157: LIFE SCIENCE: AN ENVIRONMENTAL APPROACH (Trophic Relationships)

Explore the concept of energy in biology, including the laws of thermodynamics, Earth's energy sources, how organisms obtain energy, and the dynamics of trophic relationships. Learn about food chains, food webs, and the factors that limit the number of trophic levels in ecosystems.

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BIOLOGY 157: LIFE SCIENCE: AN ENVIRONMENTAL APPROACH (Trophic Relationships)

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  1. BIOLOGY 157: LIFE SCIENCE: AN ENVIRONMENTAL APPROACH (Trophic Relationships)

  2. ENERGY • Energy is the ability to do work. • It has many forms (kinetic, potential; electrical, chemical, heat, light, etc.). • Every organism must have energy in order to function. • To understand about energy it is useful to look at a paraphrasing of the TWO ‘LAWS’ OF THERMODYNAMICS.

  3. THE LAWS OF THERMODYNAMICS • (1) Energy can be changed from one form to another but is never created or destroyed (assumes matter and energy are interchangeable). • (2) No energy transformation is 100% efficient. Some energy always goes off as unusable or unavailable forms (e.g. - when burning something to get heat, we get some light; or when metabolizing foods to get chemical energy for the running of the cells we also get some heat).

  4. EARTH’S ENERGY SOURCES • 1) the energy stored in its core • 2) the sun The equation for photosynthesis (one of the most important chemical reactions on earth): 6CO2 + 12H2O    C6H12O6 + 6H2O + 6O2 chlorophyll glucose sunlight

  5. HOW ORGANISMS GET ENERGY • AUTOTROPHS or PRODUCERS ( = self-nourishing) Photoautotrophs Chemoautotrophs • HETEROTROPHS (= other nourishing) • CONSUMERS • Herbivores • Carnivores • Omnivores • DECOMPOSERS (= REDUCERS or SAPROTROPHS)

  6. “FOOD” DEFINED • A “FOOD” is an energy rich organic compound used to fuel the metabolism of an organism. • Autotrophs make foods using simple inorganic compounds and an energy source. • Examples of inorganic compounds: water, carbon dioxide, iron, nitrates, phosphates • Examples of foods: proteins, fats, alcohols, carbohydrates such as sugars and starch

  7. TROPHIC RELATIONSHIPS (I) • TROPHIC (from the Greek meaning to nourish):essentially “Trophic Relationships” refers to energy relationships between organisms (how energy is transferred from one organism to another). • TROPHIC LEVEL:the organism’s place in the energy flow pattern in relation to the ultimate energy source. (It usually is expressed as a whole number.)

  8. TROPHIC RELATIONSHIPS (II) • The flow of energy from organism to organism (usually by eating and being eaten) forms a linear energy flow system known as a FOOD CHAIN. • In nature food chains are always interconnected to form FOOD WEBS. • The number of trophic levels in an energy flow system is limited by the ENERGY BUDGET which itself is the result of the Laws of Thermodynamics.

  9. HYPOTHETICAL FOOD CHAIN Trophic Level 1 Producer Green Plants  2 Herbivore Rabbits (= primary consumer)  3 Carnivore Snake (= secondary consumer) (= primary carnivore)  4 Carnivore Hawk (= tertiary consumer) (= secondary carnivore)  5 Carnivore Wolf (= quartenary consumer) (= tertiary carnivore)  6 Carnivore Human (= pentenary consumer) (= quartenary carnivore)

  10. EXAMPLES OF FOOD CHAINS

  11. EXAMPLE OF A FOOD WEB (I)

  12. EXAMPLE OF A FOOD WEB (II)

  13. WHAT LIMITS THE NUMBER OF TROPHIC LEVELS ? THE ENERGY BUDGET !

  14. ENERGY TRANSFER IN A FOOD CHAIN (see your last page)

  15. TROPHIC COMPLEXITY • trophic complexity = community complexity • simple systems are usually less stable • In other words, COMPLEXITY of energy flow pattern (= food web complexity), generally makes for a more stable system • WHY?

  16. ADDITIONAL things from chapter 2 for YOU to investigate • What is Entropy? • What is the connection between food and potential energy? • Which pyramid type (biomass, energy or numbers) always gives the best ‘picture’ of the trophic structure of a system? Why? • What trophic level can’t a scavenger occupy? • Most extremophiles are what type of organism?

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